Ampeg SVT-III Pro issue

[Alex R]

I have an Ampeg SVTIII Pro here on which quite a lot of DC (maybe 25v) appears in a brief burst on the output when you twiddle the 'tube gain' control... which has little other effect.

I have a preamp and a power amp schematic page, gleaned from earlier threads here, but the 'tube gain' control is on neither.

I'd very much appreciate either any thoughts - or the schematic page with the 'tube gain' control.

Thanks in advance...

[Alex R]

Answering myself here - ok I worked out/read that the tube gain control actually alters the HT to the preamp valves. Found all the schematics here

http://music-electronics-forum.com/s...ight=svt-3+pro. Thanks Enzo! Power amp schemo attached.

And some buzz and cutouts are normal when you twiddle the tube gain. Don't know about the DC movement on the output - but DC certainly shifts at the pin 1/8 connection on V2, so I guess C6 and & C7 pass that voltage change as AC, and move the bias around a bit, so that causes a quick bit of temporary DC on the output? So it's normal?

Thank for educatively not answering, made me think!